The precise mechanisms governing post-transfusion immunomodulation have not yet to be defined. The appearance of soluble type I Human leukocytes Antigen (HLA) molecules (sHLA-I), the FAS ligand (FAS-L) or cluster designation 40 (CD40-L) in the supernatant of PRBCs along the storage of blood products may be involved in such phenomena. These molecules are capable of activating or triggering the death of innate or adaptive immunity cells, especially the Natural Killer (NK) cells.